In general, the data field in account block can be used to carry any info when sending transactions through tx_sendRawTx API.
In order to utilize or display the carried data correctly, it is necessary to describe the data content type in uniform way.

The proposal suggests to append 2 bytes content type at beginning to indicate what type of data is followed.

Content type is a uint16 number stored in big endian format.
Please note that types 1(0x0001) - 2048(0x0800) are officially reserved and should not be used by third party.

Restriction

It is known that content type might not be correctly recognized under the situation calling a smart contract, due to occasional conflict with method hash, which occupies the first few bytes of data field.